I got a Vortex Smart (with the newest firmware). It's calibrated, so everything should be set up right.
When I starte a slope workout, everything is fine, until i start to increase the slope. The watt drops pretty hard.
Also when I'm doing the FTP test i got only 78 watt of power. Normally I'm around 130-150ish. Do i have a problem with slope?
Cycling with slope is also very unrhythmic. Does maybe the wheel slip through?

Slipping can certainly cause a surging feeling. I would try increasing the tension on the tire. Do small 1/4 counterclockwise turns of the tension knob (after releasing the tension lever). I would keep the tire pressure on the high side. You should also clean the roller and tire. A trainer tire works best, but a road tire is fine if it is kept clean.

Do not worry if the new calibration is a bit high or slightly into the red zone. Calibration zone is only a guideline.

Your are the best!
I'm total new to cycling and thought this calibration thing must be in the middle to be perfect.
I cleaned everything and put on more pressure. Now it works perfect.
thank you so much!